On-demand packet discard scheme for TCP over ATM-UBR service

Abstract

The performance of the TCP over ATM networks is investigated. A TCP packet is segmented into multiple ATM cells at the sending node and reassembled at the receiving node. When congestion occurs, the ATM switch may drop some of the cells. If one or more cells of a TCP packet are dropped, the TCP packet is said to be corrupted. A corrupted packet will be discarded at the receiving node. Transmitting the cells of a corrupted packet will only waste network resources and lower the effective throughput. A major objective of a selective packet discard scheme is to minimise the packet fragmentation problem. Previous approaches such as the early packet discard (EPD) scheme and its variants may drop incoming cells when congestion is anticipated. As a result, the buffer is under-utilised most of the time. Packets may be dropped unnecessarily, and the fragmentation problem cannot be avoided. A new packet discard scheme, called the on-demand packet discard (ODPD) scheme, is presented by the author. The ODPD scheme can fully utilise the available buffer space and effectively avoid the fragmentation problem. The performance of ODPD is found to be better than EPD and its variants under all traffic conditions.